One of the problems facing clinicians who deal with victims of vertebral injury is determining whether the vertebral column is stable. The subject of stability is a source of controversy among spine surgeons as well as radiologists. Physicians dealing with vertebral injuries need to know specific information: the presence and location of all fractures, whether there is encroachment of the vertebral canal or neural foramina by bone or herniated disc fragments, and the results of imaging assessment of vertebral stability. As a rule, the decision of whether or not operative intervention is needed rests on the issues of encroachment and vertebral stability. Stability of the vertebral column depends on the integrity of the major skeletal components, the intervertebral discs, facet joints, and the ligaments (Fig. 10.1) [1–3]. Stability is defined as the ability of the vertebral column to maintain its normal alignment, to provide support for the head and torso, and to protect the neural elements under normal physiologic stress [3]. Unstable injuries are those that have the potential to cause progressive neurologic deterioration or skeletal deformity under normal physiologic motion or loading [3]. If the instability is in the craniocervical junction, death may be a consequence.

For a lesion to be considered unstable, enough damage must have occurred to allow abnormal motion at, above, or below the site(s) of injury. Disruption of any one of the elements mentioned above may not necessarily produce an unstable injury; it is generally a combination of abnormalities that results in instability [4–7].